A saponified ethylene-vinyl ester copolymer (hereinafter, also called as “EVOH resin”) has superior gas-barrier properties, similarly to polyvinyl alcohol (hereinafter, also called as “PVA”) obtained by saponification of polyvinyl ester. Whereas PVA is water-soluble and a PVA film cannot be produced by melt-forming because the melting point of PVA is close to the decomposition point thereof, EVOH resin is water-insoluble and an EVOH resin film can be produced by melt-forming, because a difference between the melting point and the decomposition point of EVOH resin is large. In view of the above, EVOH resin is widely used for various packaging materials such as food packaging materials and medical packaging materials. An EVOH resin film may be used alone. However, because the gas-barrier properties and film strength of the EVOH resin film may be degraded resulting from moisture absorbing, the EVOH resin film is normally used as a multilayer structure, wherein an outer surface layer is constituted of e.g. a thermoplastic resin film having less water permeability.
A multilayer structure such as a sheet may preferably be stretched to increase the strength thereof. Stretching an EVOH resin layer enables to enhance the gas-barrier properties, because the molecular chains are aligned in a high density state by stretching. In view of this, the multilayer structure is normally stretched for use.
The stretchability of the EVOH resin layer is poor, as compared with that of a thermoplastic resin layer. Accordingly, in stretching a multilayer structure including an EVOH resin layer by e.g. uniaxial stretching or biaxial stretching, it is difficult to evenly stretch the EVOH resin layer, and stretching the EVOH resin layer cannot follow stretching the outer surface layer. As a result, the stretched multilayer structure may have streaks, or in a worse case, may be ruptured.
In order to enhance the stretchability of the multilayer structure including an EVOH resin layer, for instance, JP S63-114645A suggests an EVOH resin composition comprising a specific polyamide resin and EVOH resin, as a suitable material of the multilayer structure.
JP H08-311276A suggests an EVOH resin composition comprising two kinds of EVOH resins having an ethylene content different from each other.    [Patent document 1] JP S63-114645A    [Patent document 2] JP H08-311276A